In the field of optical display technology it is desirable to provide uniform, bright and efficient illumination. Some displays in the past have been relatively brighter at one or more portions and relatively less bright at others. It would be desirable to provide for substantially uniform illumination brightness across the area of an optical display. Some displays in the past have presented different color effects across the face. It is desirable to provide for substantially uniform color across the area or face of a display.
Some prior optical displays have required relatively large dimensions in order to distribute uniformly over the surface of the display illuminating or incident light. However, it often is desirable to minimize such display dimensions. For example, in the field of head mounted displays, such as those used in the field of virtual reality, heads-up display technology, etc. where the display is mounted on the head of an observer, it is desirable to minimize the size and weight of the display and the illuminating source.
Various techniques have been used in the past to improve efficiency of light illumination systems for displays and for the developing of light output by the display for viewing. For example, in some prior displays the intensity of the output light may be as small as only a few percent of the intensity of the illumination source for the display. It would desirable to increase the amount of output light able to be produced by a display relative to the amount of input light provided the display.
One of the problems in conventional liquid crystal displays, such as twisted nematic liquid crystal displays, is the inefficiency in light usage. Since the light usually needs to go through two polarizers, and additional color filters for color displays, the output light often only is two to four percent of the intensity of the incident light from the illuminating source. In liquid crystal television and computer displays, for example, the display is a transmissive one; the light source is on one side of the display while the viewer views the display from the opposite side. The losses in light in such systems are substantial and, therefore, such systems require a substantial amount of power for the light source to provide adequate illumination for satisfactory viewing. If the light source is supplied by battery power, usually the battery life is relatively short because of such substantial power requirement. It would be desirable to improve illumination efficiency for displays and, therefore, to increase battery life for such displays and systems using them.
Various head mounted displays and optical systems have been developed in the past. The present invention is useful to provide illumination for head mounted displays and for other types of displays.
The present invention may be used in an optical system or in a display system in which a common image is provided to both eyes of a person, and the invention also may be used in devices and displays in which different images are provided to respective eyes of a person. When different images are provided, they may be coordinated or not; when they are coordinated, though, they may be so coordinated so as to provide three dimensional or stereoscopic imaging. The invention also may be used with projection displays or as part of a projection display.